Conifers

Biology
COPYRIGHT 2002 The Gale Group Inc.

Conifers

The conifers are a group of about 588 species of trees and shrubs that include many of the best-known plants in the world. All conifers bear seeds inside cones, woody protective structures. There are seven families of conifers. The largest is the Pine family (232 species), which includes such familiar trees as pine, spruce, fir, and larch. Most plants in this family have needlelike foliage and bear their seeds in a cone formed of papery or woody scales whorled about a central axis. The Pine family includes the oldest known trees, the bristlecone pines, many of which are known to be more than four thousand years old.

The next largest family (147 species) is the Podocarps. Most Podocarps are tropical trees, many of them native to the Southern Hemisphere. Generally, they have broad leaves and bear their seeds in a structure similar to a berry. Nonetheless, their flowers, the anatomy of their wood, and the details of seed development all show that Podocarps are closely related to the Cypress family (141 species).

Most trees in the Cypress family bear scalelike foliage and have cones that have only a few scales. Besides cypress, this diverse family includes juniper, a common tree or shrub in desert areas; giant sequoia, which is the world's largest tree; and coast redwood, the tallest tree in the world. The remaining 68 species of conifers include a wide variety of less well-known trees, such as the yews, which are common garden plants, and the araucarias, which are important timber trees in some tropical countries.

Although the 588 species of conifers are not a very abundant group compared with the 250,000 species of flowering plants, the conifers are ecologically and economically one of the most important plant groups. A few species in the Pine family form the most extensive forest on Earth, the boreal forest, which covers thousands of miles across Russia, Canada, and Scandinavia. One species, the Siberian larch, is the most numerous and widespread of all trees.

Almost all conifers are trees, and so they create forests that provide habitat for wildlife and a wide variety of insects, fungi, and smaller plants. Some conifer forests support extremely complex ecosystems with very high levels of biodiversity. Conifers are also very important economically because they provide wood and wood products that are used to make buildings, furniture, and paper. Before petroleum was widely used, conifers were also the
source of many important organic chemicals used to make paint and other finishes, solvents, and oils used by industry. Native peoples have used conifers to make houses and necessary implements, and some peoples have even used them for clothing (from woven bark) and food (seeds).

Conifers are one of the oldest groups of plants, with araucaria-like trees first appearing about 290 million years ago, and primitive representatives of most of the conifer families appearing during the Mesozoic era, from 230 to 68 million years ago. Therefore, conifers, and other types of gymnosperms , are generally regarded as being more evolutionarily primitive than angiosperms.

Conifers

Plant Sciences
COPYRIGHT 2001 The Gale Group Inc.

Conifers

Conifers are the largest, most widespread, and most economically important group of gymnosperms (nonflowering seed plants), including about 630 species divided into six or seven families. Conifers are the oldest extant group of seed plants, dating back to more than 280 million years in the fossil record. Some of the current families and genera have long fossil records; for example, remarkably well-preserved and modern-appearing cones of the genus Araucaria dating to 160 million years ago have been discovered, and a well-preserved fossil pine cone dating to 130 million years ago can be compared directly with cones of living pine trees.

Conifer Diversity

All conifers are woody plants, mostly trees or sometimes shrubs. Typical conifers such as members of the pine, cypress, and araucaria families are recognized by their woody seed cones, with flattened or shield-shape cone scales arranged spirally or in pairs or whorls around a central axis. The woody-coned conifers usually have winged seeds that are dispersed by wind and gravity. Other important groups of conifers such as the yew family, junipers, and most of the podocarp family have their seed cones reduced to one- or few-seeded fleshy structures that are dispersed by birds. Conifer seed cones range from less than 1 centimeter in length to up to 50 centimeters long and may be quite massive in some species of pines and araucarias.

Most conifers are evergreen, but a few genera (notably bald cypress, dawn redwood, and larch) shed their leaves during the winter. The majority of conifers have narrow, needle-shaped leaves, arranged in spirals or sometimes in pairs, or are found in tightly clustered whorls on short branches. Pines are unusual in having their leaves extremely tightly clustered in needle clusters (fascicles) with almost no stem elongation between the leaves. Some conifers have their leaves very reduced and scalelike (most of the cypress family), while subtropical to tropical conifers in the podocarp and araucaria families may have the leaves flattened and are relatively broad.

Conifers include some of the longest-living, tallest, and most massive trees in the world. Bristlecone pines from the southwestern United States are among the longest living individual trees in the world, having been dated from tree rings to more than five thousand years in age. Sequoias are among the tallest trees in the world, reaching more than 110 meters in height, while the related giant sequoia reaches 106 meters in height and up to 11 meters in diameter. Large and ancient specimens of conifers are featured attractions

in national parks in many parts of the world, most notably sequoias and giant sequoias in California, alerce (Fitzroya ) in Chile and Argentina, and kauri (Agathis ) in New Zealand.

Conifer Distribution

Conifers are important forest components in many areas of the world, and members of the pine family are especially abundant in cool to cold-temperate and mountainous areas of the Northern Hemisphere, where such genera as pines, spruces, firs, and hemlocks often form dense forests. Junipers and pines are also very abundant trees in semiarid environments of the Northern Hemisphere such as the Great Basin region of the western United States. Pines are the most widely distributed genus of trees in the Northern Hemisphere and are also especially widely planted as timber trees in both hemispheres.

Several genera of conifers with only a single living species of very restricted distribution were once much more widespread in the fossil record and have been termed "living fossils." These include the dawn redwood (Metasequoia ) from China and the sequoia and giant sequoia from California. Another remarkable genus, Wollemia (from the araucaria family), was known only as a fossil from Australia until 1994, when a living plant of this species was discovered growing in a remote canyon area near Sydney, Australia.

Economic Uses

Conifers are extremely important economically as sources of lumber and other wood products, and are also widely planted as ornamental trees and shrubs. The most important sources of softwood lumber in the world are
trees in the pine family, especially species of pine, spruce, larch, and Douglas-fir, which are widely used for dimensional timber for building construction and boat building, and for general construction uses such as utility poles, doors, and cabinetry. These woods are also widely used for plywood and veneer and as sources of wood pulp for paper and cardboard and other modified wood products, such as charcoal. Southern yellow pines, such as slash pine and loblolly pine, are widely grown in their native southeastern United States as sources of lumber and pulp, while the Monterey pine from coastal California is now widely planted as a commercial timber tree in the Southern Hemisphere. Douglas-fir (Pseudotsuga menziesii ) is a particularly important timber species in the northwestern United States and Canada. Several species of pines are tapped or cut and steam-distilled for stem resins, which are used as commercial sources of turpentine, tar oils, rosin, and pitch. Wood of the Norway spruce and white spruce has also been prized for constructing musical instruments such as violins, and the light, strong wood of Sitka spruce has been used for aircraft construction. The attractive reddish-colored wood from species of the cypress family, such as the sequoia, is quite weather- and decay-resistant and is highly prized for building construction,
decks, fences, and other outdoor uses. Wood of the western red cedar (Thuja plicata ) has been heavily used for weather-resistant roof shingles. Fragrant wood from junipers has natural insect-repellent properties and is used for moth-resistant cedar closets or chests. Wood of juniper and incense cedar has been commonly used to make pencils.

Many species of conifers are grown as ornamentals, and a wide variety of cultivated shrub forms have been selected for garden use from members of the yew and cypress families, including several species of yew, juniper, cypress, and golden cypress (Chamaecyparis ). Conifers from a number of genera are prized as ornamental trees, of which some particularly attractive examples are the blue spruce (Picea pungens ), the Himalayan cedar (Cedrus deodara ), and the Norfolk Island pine (Araucaria heterophylla ). Several species of firs and pines are commercially grown and cut as Christmas trees, and young plants of the subtropical Norfolk Island pine are grown for indoor use as living Christmas trees. Several species of pines from Eurasia and North America are highly esteemed as sources of oil-rich edible seeds (pignoli or pine nuts). Cones of Juniperus communis (juniper berries) are used as flavorings in cooking and provide the aromatic flavoring of gin, whose name is derived through the Dutch jenever from the name of juniper. Recently, bark and leaves of several species of yews have become important as the source of taxol and related alkaloids, which disrupt the process of cell division and are used in the treatment of several types of cancer.